Abstract: An observation is demonstrated that Au/S target,triggered by gallium ion beam (69Ga＋) under experiment of high performance secondary ion mass spectrometry (TOF SIMS),does emit a considerable species of cluster negative ions with general formula of Au1－15S0－5(see Fig.1 and Table 1).Among them,a series of cluster ions with compositions of Au1－15S1－5 is recognized as AuS binary cluster ions,while other series with Au1－15 belongs to monocluster ions of pure gold,appearing in strong oddpredominance of their intensities with number of gold atom (see Fig.2).The AuS cluster ions can be characterized,in some aspects,by existence of the oddpredominance with magnitudes of gold atom (see Fig.3),inherited from the Au monoclusters; by lack of stoichiometric feature,showing that gold atoms range from 1 to 15 but sulfur atoms are always limited to 5 (see Table 1); by void of predominance as compositions as MenSn (for example,CunSn,see Table 2) or MenNn whose priority has been proved as an important feature prevailing in other binary cluster ions of metals (Me) plus sulfur (S) or other nonmetals (N); and by presence of special profiles as similar as those of CP binary cluster ions,a series of typical nonmetalbinary ones (see,Ref.23).These facts suggest that the speciation of AuS cluster ions probably comes from a constitution of relatively intact Au monoclusters,and thus imply in gaseousphase mechanism that a binary aggregation between Au monoclusters and S monoclusters or the confined polysulfur units might contribute to the formation of the AuS binary cluster ions.The aggregation may be based on covalent bindings between the end groups of the two clusters,or on a noncovalent interaction between the clusters,such as electrostatic gravitation between heteroatoms or heteromolecules,but its true mechanism remains to be resolved in future work.

Key words: Au-S binary clusteri ons, Au monocluster, Five-sulfur units, 　Aggregation, Cluster negative ions, Compositional characterization, 　　TOF SIMS